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Staggered Truss: not as Painful as it Sounds






 -by Lynn Becker

[April 25, 2008] - A new hotel brings an innovative engineering technique to Chicago. Iconic architecture to follow.


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Concrete is king. For every new steel-framed tower like the 44 story 353 North Clark Street, there's got to be at least dozen similar skyscrapers using concrete construction. But when Miglin Properties was looking for a way to make their new 207 room Staybridge Suite Hotel in River North stand out, they turned to a structural design that would bring the first staggered truss steel building to Chicago.

The $42 million project evolved out of a 2003 American Institute for Steel Construction study for a hotel using the staggered truss system. As the name Model, Staybridge Suite Hotel, Chicago, American Institute of Steel Constructionimplies, that system involves the use of full-story, 9 foot, three inch high trusses spanning the entire width of the building, staggered in position from floor to floor.

Two things made the concept attractive to Miglin. First was economy. The trusses are lightweight, easing the requirements for the foundation. Fewer interior columns are required, making for more open floor plans. At Staybridge, the system is erected with a diaphragm of precast hollow core concrete planking, providing semi-finished ceilings and floors in one shot. In the end, the project wound using 115 trusses, with 815 tons of steel.

The second advantage is speed. The trusses are fabricated off-site, making all-Truss, Staybridge Suites, Chicago, American Institute of Steel Construction, Structural Affiliates International, Valerio Dewalt Trainweather construction possible. The steel structure rests atop a four-story, poured-in-place concrete podium, with an entry lobby, two floors of parking and a fourth floor sky lobby, topped by twelve stories of hotel rooms. At the point where concrete and steel structures merge, the steel columns are embedded in two floors of concrete.

At Staybridge, the engineers came first. Miglin brought in Structural Affiliates International out of Nashville, which already had substantial experience with staggered steel trusses. Not long after, Valerio Dewalt Train was brought in as architects.

"You can see that this is very unique," said SAI Structural Engineer Socrates Ioannides at a February AISC symposium on the project. "AISC gets involved, the structural engineer gets involved, before there is even an architect, but I'm glad that we brought in the architect when we did, because you can see the difference as I go through the history here of what it would have looked like if we had not had a good architect."

Staybridge was a case of "structure as form giver."

Staybridge Suites, Chicago

"First in the process," VDT project architect Matt Dumich said at the symposium, "we needed to work with SAI and AISC to understand as architects what a staggered truss system was and what the principles were. As you can see, this is not your typical post and beam structure. We were tasked to create a distinctive architecture on this prominent site on LaSalle Street in Chicago. The design was anStaybridge Suites, Chicago, early concepts, Valerio Dewalt Train, architects evolutionary process."

One early concept, shown here, stressed the building's verticality. According to Dumich, VDT was "looking to create an iconic structure. . . Our big idea was to use the structural system and the depth of the trusses to create cantilevered floors and stagger the whole building in both directions."

Ultimately, the cantilever was confined to the south elevation where, on floors nine through thirteen, the building extends forward an additional seven feet, six inches. But by shifting those floors to the south, a cutout is created along the opposite elevation that makes the four floors above it appear to be a second cantilever, this time to the north.
Staybridge Suites, Chicago

The long north and south elevations, at 186 feet almost identical to the building's final height, are to be clad in aluminum panels, while the shorter east and west elevations will consist of a glass curtain wall. Exposed trusses create another cutout in the western facade at floors ten through thirteen, while a another exposed truss in a shallow recess on the fourth floor reads as a giant "M", which Ioannides notes not only makes the unique structure apparent, but also serves as a subtle branding of the building with the Miglin initial.
Staybridge Suites, Chicago

Dumich describes his project as "sexy," and for once that designation may not just be hype. Amidst neighbors like the classical Catholic Charities Building and the Hotel Wacker, Staybridge, when it's completed early next year, looks to give staid LaSalle a distinctive contemporary kick.
Staybridge Suites Hotel, Chicago, Valerio Dewalt Train, architects

(The AISC has a entire webpage on the project that includes multiple Powerpoints and a number of videos of the presentations made at the February symposium. Word to the wise: download and view rather than watching them crawl through your browser.)

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© 2008 photos and text Lynn Becker All rights reserved.

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